ST STM32L0x3

Reset and clock control (RCC) RM0367
218/1043 RM0367 Rev 7
Bits 31:27 Reserved, must be kept at reset value.
Bit26 HSI48SEL: 48 MHz HSI48 clock source selection bit
This bit is set and cleared by software to select the HSI48 clock source for USB and RNG.
0: PLL USB clock selected as HSI48 clock
1: RC48 clock selected as HSI48 clock
Bits 25:20 Reserved, must be kept at reset value.
Bits 19:18 LPTIM1SEL: Low-power Timer clock source selection bits
This bit is set and cleared by software.
00: APB clock selected as LP Timer clock
01: LSI clock selected as LP Timer clock
10: HSI16 clock selected as LP Timer clock
11: LSE clock selected as LP Timer clock
Bits 17:16
I2C3SEL: I2C3 clock source selection bits
This bit is set and cleared by software.
00: APB clock selected as I2C3 clock
01: System clock selected as I2C3 clock
10: HSI16 clock selected as I2C3 clock
11: not used
Bits 15:14 Reserved, must be kept at reset value.
Bits 13:12
I2C1SEL: I2C1 clock source selection bits
This bit is set and cleared by software.
00: APB clock selected as I2C1 clock
01: System clock selected as I2C1 clock
10: HSI16 clock selected as I2C1 clock
11: not used
Bits 11:10
LPUART1SEL: LPUART1 clock source selection bits
This bit is set and cleared by software.
00: APB clock selected as LPUART1 clock
01: System clock selected as LPUART1 clock
10: HSI16 clock selected as LPUART1 clock
11: LSE clock selected as LPUART1 clock
Bits 9:4 Reserved, must be kept at reset value.
Bits 3:2
USART2SEL: USART2 clock source selection bits
This bit is set and cleared by software.
00: APB clock selected as USART2 clock
01: System clock selected as USART2 clock
10: HSI16 clock selected as USART2 clock
11: LSE clock selected as USART2 clock
Bits 1:0
USART1SEL: USART1 clock source selection bits
This bit is set and cleared by software.
00: APB clock selected as USART1 clock
01: System clock selected as USART1 clock
10: HSI16 clock selected as USART1 clock
11: LSE clock selected as USART1 clock